A point-to-multipoint connection is typically used for distributing a program such as a video film or video conference, from a program source to a great number of subscribers over a telecommunication network. The act of distributing the same information to several subscribers is sometimes referred to as multicasting.
Other examples of multicasted programs are conceivable. A teacher's lesson in the form of a video lesson is one example. Another example is reading aloud from a book, such reading being transmitted, from a local library for example, over the phone or over a video network.
Depending on the geographical extent of the telecommunications network the program may be distributed nation wide, state wide or metropolitan wide.
Subscribers that want to view/listen to a multicasted program request this service by keying, at an access unit, a particular code sequence which identifies the multicast service and the particular program. Once a subscriber has done this a connection is set up between the subscriber and the program source. The program is delivered to the subscriber using this connection and the subscriber views/listens to the program at a terminal unit, such as for example a television set. When the subscriber no longer wants to view/listen to the program she/he requests the connection be released by keying in another code sequence at her/his access unit. The access unit as well as the terminal unit are located in the subscriber's home.
It is possible to simultaneously distribute, in one and the same telecommunication network, different programs from different origin points within the telecommunication network.
To-day a program is distributed from a common origin to several subscribers by setting up individual point-to-point connections to each of said subscribers. Several such point-to-point connections may have a common route along which the same program is transmitted. Along said common route the same program is transmitted in parallel using several different connections. This is a waste of resources of the telecommunication network, since every point-to-point connection requires its own resources. Said resources comprise i.a. time slots in physical lines, exchange terminals, inlet and outlet ports in exchanges. Also the capacity of exchanges which are situated along such a common route is reduced in the sense that less calls, not related to the distributed program, can be switched.